An armblade is a magic weapon that attaches to your arm, becoming inseparable from you as long as you're attuned to it. To attune to this item, you must hold it against your forearm for the entire attunement period.
As a bonus action, you can retract the armblade into your forearm or extend it from there. While it is extended, you can use the weapon as if you were holding it, and you can't use that hand for other purposes.
When making an attack with a Finesse weapon, use your choice of your Strength or Dexterity modifier for the attack and damage rolls. You must use the same modifier for both rolls.
A Reach weapon adds 5 feet to your reach when you attack with it, as well as when determining your reach for Opportunity Attack with it.
If you hit a creature with this weapon and deal damage to it, you can reduce its Speed by 10 feet until the start of your next turn. If the creature is hit more than once by weapons that have this property, the Speed reduction doesn't exceed 10 feet.